How to Find Your Formula for Insulin and Food Around Workouts

Like most people with diabetes, I tend to have a love/hate relationship with cardio. I love all the positive things that cardio does for my body and diabetes management, but I hate how hard it can be to keep my blood sugars under control while working out.

At least I used to hate it, before I found a formula for insulin and food around workouts that works for me (most of the time).

In this post, I’ll describe how you can find your own formula for success when it comes to cardio.

Why do cardio at all if it’s so hard?

Regular cardio workouts have so many benefits that they should always be included in your weekly workout schedule, regardless of your goals. Cardio can help with weight management, improves insulin sensitivity, help you relax and sleep better, and improves your cardiac health. All great things!

The general guidelines state that healthy adults should engage in at least 150 minutes of exercise per week. That’s only 20 min of movement per day. It doesn’t have to be full-out “I think I’m going to die” cardio either. Just getting your heart rate elevated for this period of time is enough to reap most of the benefits.

Take me, for example – some of my favorite types of cardio are dancing, hiking, circuit training, walking the dog, and boxing. I recently gave spinning a try, and though I really wanted to love it, after 7 spinning classes I just had to admit that I didn’t enjoy it at all. So I won’t be doing that again anytime soon.

What I’m trying to say is that cardio can be challenging and fun at the same time, and you should choose a type of cardio that you enjoy!

Taming your blood sugars during and after cardio

When somebody with a functioning pancreas starts a cardio session, his or her body will reduce the amount of insulin released. The body is smart like that. However, those of us who take insulin have to be smart on behalf of our bodies and adjust our insulin when doing cardio.

What happens when you start a steady-state cardio session (meaning you’re not doing intervals but keeping your heart rate elevated and fairly stable) is that your insulin sensitivity increases. In other words, your body gets more efficient at using the insulin you’ve injected (can we all just agree that your body becoming more efficient is a good thing, please?).

This improved efficiency is why you will most likely need less insulin when adding cardio workouts to your weekly routine.

Yes, I said you’ll need less insulin!

This is one of the most important things that I teach all my clients. If you are consistently experiencing lows during cardio (or in general), it’s generally better to reduce your insulin rather than increase your daily intake of carbs. This can mean a reduction in your bolus amounts, your basal amounts, or both.

If you try to fight lows by preemptively eating carbs, you are just “feeding the insulin”, which can be counterproductive, is more difficult to get right, and can make weight management much harder.

How much to adjust your insulin

The question then, is when and how much to adjust your insulin. You don’t want to reduce it too much and have your blood sugars running high either. Unfortunately, there is no easy formula that fits everyone, but if you track what you are doing and analyze your data, you can find your own formula for successful cardio and diabetes management. You can use my free Blood Glucose tracker (PDF or Excel), or make your own.

Note: While there isn’t a formula that fits all, there are some general guidelines that I highly recommend you take note of!

The three golden rules for gathering data:

Reduce the number of variables – do the same exercise routine the first week or so. If you can also keep your active insulin on board when exercising the same, even better, but it’s not a requirement

Measure, measure, measure – as a minimum you will have to test your blood sugar before your workout, right after, and 60-90 min after

Accept missteps – it’s most likely that you won’t get it right every time, and that’s OK. Keep glucose tabs around and learn from your mistakes

How to find your diabetes management formula

Let’s get to it. If you follow the three golden rules above, you should be able to start putting your formula together after as little as 2-3 cardio sessions. What I want you to do is pretty simple. I want you to track your blood sugars religiously, following the same format as I have in my BG tracker. I’ve added an example in the tracker so that you can see what that would look like, and I’ll use that example here.

(I know it’s hard to read clearly here, but you can see a larger version if you click the image or download the tracker)

This example assumes I worked out Monday and Wednesday, doing cardio for 40 minutes in the evening on both days. In this example, my assessment would be that I managed to get my insulin right on Monday, but that I had too much insulin in my system for the Wednesday session (I went low and had to drink juice).

The only reason why my blood sugar was acceptable 60 minutes after the workout Wednesday was due to the extra carbs I had during my workout, and that isn’t optimal management. I had to have that juice not because I was thirsty or craving juice, but because I needed to feed the insulin in my system, of which there was too much. That indicates that something has to change.

There are only two data points, but based on this, I would try to have less than 0.5 IU active insulin on board when starting a cardio session like the ones I did that week. Note that the low blood sugar during the Wednesday workout could also be due to already declining sugars due to overdosing at dinner. That would be something I would have to test out as I continued to do more workouts.

What I did here was record my findings, make an initial analysis, and form a few hypotheses based on my findings (e.g. of a hypothesis is to not have more than 0.5 IU active insulin on board). If you’re self-managed like me, you can then start making adjustments and test out your hypothesis. If you rely on your medical team for adjustments, this will be golden information to bring to them so you can make the changes together.

There are generally 3 things your hypothesis could be centered around when it comes to making insulin adjustments for cardio: mealtime bolus adjustments, amount of active insulin on board during the workout, and basal adjustments.

Please always be cautious when making changes to your diabetes management. If you feel that you need more data points before making any hypotheses or tweaks to your insulin doses (if this is new to you, I would definitely recommend minimum five data points), please do so. If you don’t make insulin adjustments on your own but with your medical team, please bring them your data and continue to work with them.

No matter what, this is a process that takes time. You will have successes and missteps, but after a while, you will start to have a very good idea of how to adjust your insulin to get through a cardio workout safely and effectively!

About Christel Oerum

Christel is a passionate fitness enthusiast and the co-founder of Diabetes Strong. She is a Certified Personal Trainer specializing in diabetes. As someone living with type 1 diabetes, Christel is particularly passionate about helping others with diabetes live active healthy lives. She’s a diabetes advocate, public speaker, and author of the popular diabetes book Fit With Diabetes.

Reader Interactions

Comments

Hi,
I’ve been reading a lot of articles on this site and I really love them! My question is how do I figure out how to keep my blood sugars from being all over the place when exercising when I take injections? I’ve been a type 1 since I was 10 years old, so going on 16 years now and had a pump until I was around 20. I’m extremely sensitive to just about everything it seems so exercise has been really difficult, especially without a pump. I take Lantus twice a day (24 units in the morning and 8 at night) and I also take Humalog. Recently, I’ve started walking a lot (I try to walk for at least 30 minutes every day) to try to get healthier but the problem I’m having is really terrible lows that keep dropping and dropping (ex. I’ll test and it’s 60, treat/wait, test again and I’m 52), and then ending up too high afterwards. My pens don’t have half unit increments so when I calculate corrections for highs, if I round up, I drop too low again but if I round down, I’m too high and when I decrease the amount of Lantus I take, even with walking, I still get too high. I have tried eating a snack before/mid workout which normally is juice and granola. I monitor my blood sugars as closely as possible, my only activity is walking, and I try to keep it to the same amount of time each day but it still seems so random. I can’t figure out what I’m doing wrong and it’s getting frustrating! Could you suggest any help?

Annoying that you’re having such a hard time with this. My approach (and I’m on pens as well) would be to start with fasted exercise, so right after you wake up and have taken your Lantus. If you still go low, your Lantus needs to be dialed back (might even be the evening Lantus depending on when you take it). Also remember the amount of carbs you ate the day before and where you are in your cycle can impact the outcome.
When that is figured out, do afternoon workouts. Most important is to determine your IOB before your workout. Since you use pens, you’ll either have to write it down or use an app like RapidCalc to track it. Most likely you have too much IOB going if you go low.
Finally, both Humalog and Novolog is offered in 1/2 unit pens. You’ll have to use a durable pen though, but if you need 1/2 units that’s the way to go.
I know this is a lot, and that’s why this is what I focus on with a lot of my coaching clients. If you decide you need personalized support, send me a note through the coaching form here on the site

This is some great info for diabetics looking to exercise without getting lows. I have type 1 diabetes and use an insulin pump with CGM for my treatment but it still is tricky to keep sugar levels in a safe range while exercising or working out. One thing I’ve noticed is that less insulin in your body before and during exercise is always better. And you’re exactly correct when you say your insulin sensitivity increases during elevated heart rate while doing cardio cause it definitely happens to me. Thanks C 🙂

I use pens and I workout (alternating cardio and resistance) on Monday to Thursday mornings. My levels vary each morning and I need rapid insulin most mornings as hormones release glucose into my body. It is never the same though, there has been an occasional morning where I didn’t need any rapid and my hormones were not affected. I test on getting up then take a unit or 2 of rapid depending on what my glucose level is, then I often test after, I also may test mid workout if I feel it is getting low, then I always test before leaving for work as I often cycle or walk a little and then I test when I get to work. After each test, I make adjustments if I need to I.e take dextrose or take a unit of rapid if above 7. I wish it was the same every day but it never is and I can’t predict what it will be like. I just test a lot and monitor.

Sounds like you do have a bit of a pattern going and a method to making corrections. Exercise is obviously not the only variable so what you eat the day/evening before will also impact your morning BG rise. Since you are alternating the types of workouts you’ll most likely also see different impact on insulin sensitivity depending on what you did the day before.
So basically you have a LOT of variables going on which I guess is why it looks random. If you want to get into the details I suggest you try and single some variables out (like only look at cardio days coming after a resistance training day and trying to keep the food the same) and you could start to see patterns. It’s a lot of work, but I’ve found that it’s worth it

Hi Ivan,
If you still drop despite more carbs and reduction in insulin you might have to be even more aggressive when it comes to your insulin reduction. If you’re on a pump it will come down to basal suspension or reduction, maybe even before exercise. If on pen, it will mainly come down to bolus reduction. If you follow my guidelines for finding your formula you should find something that works for you

If you don’t have diabetes your body will compensate for the activity preventing you going into hypoglycemia. The point of the article is to support people living with diabetes in figuring out how to do that without the help of a functioning system.
Glad you figured it out by yourself.

One variable that I removed that made a big difference is a meal bolus when trying to figure out how to deal with it. For me, because I get so sensitive(1/5->1/10 of normal needed), even at 3-4hrs, so by keepig that at least 4-5hrs I was able to better hone the basal. Then after that I used the ratio of normal/running basal as a starting point for bolusing. Testing testing testing is exactly right.